Devices designed for delivering useful agents are becoming increasingly important articles of manufacture. The devices enjoy a wide application in commerce which includes the agriculture and pharmaceutical industries. Generally, the devices operate by diffusion, and they consists of an active agent housed within an inert wall structure. If, the thermodynamic activity of the agent is maintained substantially constant in the device, then a steady state will be established with the release rate of agent from the device substantially constant over time. This is commonly referred to as zero order release, a phrase suggested by physical-chemical kinetics.
If, however, the agent is present in the device in an undersaturated amount, of if the agent is present in a saturated amount with no excess agent phase, the thermodynamic activity and concomitantly the release rate will fall exponentially over time. This activity is commonly referred to as first order release, a phrase also suggested by physical-chemical kinetics. The zero order release is the most preferred of the two different rates of release for many applications, because in many applications the amount of agent consumed as a function of time is constant, requiring a constant, zero order rate of supply of agent in order to achieve and maintain a constant desired effect over time. It will be appreciated in view of this presentation, that if a device is provided that can exhibit a substantially zero order release over time, the device would have a positive commercial use and also represent a major contribution to delivery science.